The effects of ischemia and recovery have previously been investigated in the gerbil cerebral cortex in vivo. The results have provided some evidence about the biochemical perturbations that could lead to irreversible brain damage. Of particular interest are the changes in cyclic AMP, the overshoots in P-creatine and glycogen, and the gradual restoration of the total adenylate pool. The significance of these changes to the survival of the animal are being examined in other regions of the brain that are known to be particularly susceptible to an ischemic episode. The increases in cyclic AMP both during and after ischemia can be mimicked in rat brain slices and this model is being used to identify the agonist(s) with specific receptor antagonists. Studies on the cerebral metabolism in brains from hibernating hamsters is being continued. The changes in metabolites including a reduction in cyclic GMP and an increase in GABA and lactate which appear to be directly related to hibernation have been demonstrated in other regions of the brain.